CONTROLLING A 12VDC RELAY WITH 2VDC SOURCE USING A TRANSISTER

Discussion in 'The Projects Forum' started by KENOWITCH, May 25, 2016.

  1. KENOWITCH

    Thread Starter New Member

    May 25, 2016
    1
    0
    Hi,
    Could someone have an idea on what to do if you want to switch on a 12vdc relay coil with a signal of 2vdc that is lighting up a certain LED? My setup is that I connect the 2vdc to the base of the transistor via a resistor and the connect 12vdc voltage source to the terminal A1 of the relay coil and then connect the the terminal A2 of the relay coil to the collector. Finally I connect the emitter to the ground and the I am done. Is this the right thing to do? Ideally what I want to achieve here is to have the relay coming on when the LED comes on and vice versa. Then I use the relay contacts either as digital inut signals for some control or to run some load e.g a lamp or a small motor. Please help.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    I think so, but verbal descriptions are sometimes hard to follow. For best results I suggest you come up with a schematic diagram. This is the universal language of electronics.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,561
    2,378
    Don't forget the BEMF diode across the coil.
    Also look at using a 2n7000. Mosfet.
    Max.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,804
    1,105
    Your circuit sounds right, except for one vital missing component. You need a reverse-biased diode connected across the relay coil to kill the nasty voltage spike which occurs when the coil switches off. Diode cathode goes to +12V, diode anode goes to collector. Whatever supplies current to the LED must also be able to supply the required transistor base current.
     
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